The following abbreviations and terms are herewith defined:
3GPP third generation partnership project
ACK acknowledgement
CCE control channel element
DCI downlink control information
DL downlink eNodeB base station/Node B of an LTE system
E-UTRAN evolved UTRAN
FDD frequency division duplex
HARQ hybrid automatic repeat (or retransmission) request
LTE long term evolution of 3GPP (also known as 3.9G)
LTE Rel-8 LTE Release 8 (currently being standardized)
N_DL_RB number of downlink resource blocks
N_UL_RB number of uplink resource blocks
Node B base station or similar network access node
OFDM orthogonal frequency division multiplex
PBCH physical broadcast channel
PCFICH physical control format indicator channel
PDCCH physical downlink control channel
PDSCH physical downlink shared channel
PHICH physical hybrid ARQ indicator channel
PMCH physical multicast channel
PRB physical resource block
SCH synchronization channel (primary p-SCH; secondary s-SCH)
TDD time division duplex
UE user equipment (e.g., mobile equipment/station)
UL uplink
UMTS universal mobile telecommunications system
UTRAN UMTS terrestrial radio access network
3GPP is standardizing the long-term evolution (LTE) of the radio-access technology which aims to achieve reduced latency, higher user data rates, improved system capacity and coverage, and reduced cost for the operator. The current understanding of LTE relevant to these teachings may be seen at 3GPP TR 36.213 v8.3.0 (2008-05) entitled PHYSICAL LAYER PROCEDURES (RELEASE 8). Further details of the LTE DL air interface may be seen at TS 36.211 v8.3.0, PHYSICAL CHANNELS AND MODULATION, and also at TS 36.212 v8.3.0, MULTIPLEXING AND CHANNEL CODING (both of which are Release 8).
The LTE DL air interface is based on orthogonal frequency division multiple access using the PDSCH and PMCH data channels, and also PDCCH, PCFICH, PHICH, PBCH, and primary and secondary SCH control channels. The resource mapping of these channel types depends on the downlink system'bandwidth, designated N_DL_RB, which is a configuration parameter in TS 36.211 and represents the available number of DL RBs. Below are summarized resource mapping for those channels.
Resource mapping of PCFICH. The PCFICH broadcasts the number of OFDM symbols used by the PDCCH (e.g., 1, 2, or 3). The PCFICH information consists of 32 bits coded into 16 QPSK (quaternary phase shift keying) modulation symbols which are mapped in the first OFDM symbol of the subframe as 4 symbol quadruplets to 4 equally distant (in the frequency dimension) resource element (RE) groups (of consecutive subcarriers). The position of the 4 RE groups varies with the physical cell identifier such that basically all possible RE group positions can be reached. Further details of the PCFICH resource mapping are specified at TS 36.211 v8.3.0 Section 6.7.4.
If the set of Physical Cell Identifiers is not restricted, the PCFICH in a network practically extends over the complete carrier bandwidth. An example of the resource mapping for 3 MHz bandwidth is shown at FIG. 1, with the PCFICH shown in the 1st OFDM symbol position at PRBs 2, 6, 9 and 13. Depending on the physical cell identifier, the four PCFICH portions “move” over the carrier bandwidth.
Resource mapping of PHICH. The PHICH contains the ACK/NAKs for the Uplink HARQ. Multiple PHICHs are grouped into a PHICH group and each PHICH group is mapped in symbol quadruplets to RE groups. Each PHICH group is assigned to a set of 3 Resource Element groups whose positions depend mainly on the DL system bandwidth N_DL_RB, the RE groups already covered by PCFICH, on the PHICH group index, and on the physical cell identifier. The positions of the 3 RE groups are (more or less) equidistant. Consecutive PHICH group indices are mapped to consecutive RE groups. The PHICH may either be mapped to the 1st or the first 3 OFDM symbol(s).
If the set of physical cell identifiers is not restricted, this means that the PHICH practically extends over the complete carrier frequency spectrum. Further details of the PHICH mapping are specified at TS 36.211 v8.3.0, Section 6.9.3. An example of the resource mapping for 3 MHz bandwidth is shown in FIG. 1, where one group of PCHICHs is at PRBs 1-3, another group is at PRBs 6-8, and the third group is at PRBs 11-13 (all at the 1St OFDM symbol). Depending on the physical cell identifier the three PHICH portions “move” over the carrier bandwidth.
Coding, interleaving, and resource mapping of the PDCCH. The PDCCH contains the UL and DL control information. The PDCCH is built from CCEs and maps (except for resources used by the PCFICH and the PHICH) to the full configured DL system bandwidth N_DL_RB for the 1st up to the first 3 OFDM symbols of a subframe. After each PDCCH has been channel-coded and interleaved (as referenced in TS 36.212, see Exhibit C) all PDCCH bits are concatenated and scrambled as a whole with the cell-specific scrambling sequence. Before scrambling the string is filled up with dummy elements (called NIL) to match with the DL system bandwidth (after subtraction of PCFICH and PHICH resources). Then the scrambled sequence is cut into symbol quadruplets which are interleaved in symbol quadruplet granularity first, cyclically shifted depending on the physical cell identity, and then mapped subsequently from the lowest RE group up to the highest RE group. Practically, the PDCCH extends over the complete DL system bandwidth.
Further details of the above resource mappings may be seen at TS 36.211 v8.3.0, TS 36.212 v8.3.0 and TS 36.213 v8.3.0 as referenced above.
While the PBCH and the primary and secondary SCH are centered with respect to the DC carrier using a narrow bandwidth of 6 RBs (shown PRBs 4-9 and spanning OFDM symbols 6-11 at FIG. 1), the PDCCH, the PCFICH and the PHICH extend over the complete DL system bandwidth as configured by N_DL_RB. The PDSCH and the PMCH allocations are controlled by scheduling. Further limitation of PDSCH and PMCH bandwidth beyond the configuration limit N_DL_RB can be vendor-specific and still be compliant with LTE Release 8.
The LTE DL system bandwidth could be flexibly configured if all options for N_DL_RB ranging from 6 RBs up to 110 RBs are supported. However, following the issue of 3GPP TS 36.104 v8.1.0 (2008-03) BASE STATION BS RADIO TRANSMISSION AND RECEPTION and 3GPP TS 36.101 v8.1.0 (2008-03); USER EQUIPMENT UE RADIO TRANSMISSION AND RECEPTION, only selected DL (and UL) system bandwidths are supported by the standard LTE Release 8: for the FDD mode these bandwidths are 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, and 20 MHz, and are shown along the upper row of FIG. 2. The standardized system bandwidths (both in terms of MHz as well as in terms of the number of active RBs (N_DL_RB) are given in Table 5.1-1 of TS 36.104 v8.1.0, and are shown along the lower row of FIG. 2.
The lower row of FIG. 2 are what the channel mapping is based upon, wherein the active transmission bandwidth is always 180 kHz times the number of PRBs (for example, the 5 MHz transmission bandwidth corresponds to a 4.5 MHz (=25 times 180 KHz) active transmission bandwidth). By 3GPP TS 36.104 and 36.101, manufacturers of equipment operating within a LTE Release 8 system may not fully exploit the available PRBs as long as all 3GPP specifications including the RF specifications in TS 36.104 and TS 36.101 are met such that a standard LTE Release 8 terminal and a standard LTE network can operate fully standard-compliant.
In typical coexistence situations, standardized DL system bandwidths may either lead to violations of emission limits if the selected bandwidth is too wide, or would not fully exploit the available spectrum if the selected bandwidth is too narrow. Despite the coexistence analysis report (3GPP TR 36.942 v1.2.0, 2007-06) as well as conclusive transceiver specifications for UE (TS 36.101 v8.1.0, 2008-03) and for BS (TS 36.104 v8.1.0, 2008-03), many operators face deployment situations where at least the DL system bandwidth they select cannot be matched efficiently by one of the LTE Release 8 standardized system bandwidths.
As noted above, using a standardized DL system bandwidth according to LTE Release 8 that is smaller than the operator's selected bandwidth will drastically reduce spectral efficiency, while using a standardized bandwidth that is larger than the selected bandwidth is simply not possible due to the wireless communication regulator's requirements and emission limits. Arbitrary DL system bandwidths are not supported by the standard. Simply using a combination of smaller bandwidths is seen to drastically reduce spectral efficiency both in DL and UL.
These teachings lead to a more elegant solution to the above problem (described in the following) that is seen to be much more spectrum efficient and also to remain within regulator's emission limits for which the selected bandwidths are tailored.